I've got a personal project where I want to replace an analogue meter with a 'smart' display--the idea is a bit of a feature creep in and of itself, when I was looking at swapping in an Analog Devices AD2010 (3.5 digit, +/-199.9mV DPM, 100M?, Datasheet) to an old piece of equipment.
The original meter has a 0~120 scale, with F.S. of 200uA.
My thought was to take one of these DPMs that I have, with its 100M? impedance, and putting it in parallel with a precision 600? resistor for the current division, would register '120.0' (mV) on the DPM (1.2nA through 100M?). Pretty straightforward and having 100µV resolution would be nice, too.
Now, here's where the gears started running--why use a fixed device with a fixed display? Why not employ some smart hardware and extend the usability of this device? Say I want to show the current reading and below it an average, or compare readings from one to the next, maybe shoving a 128x64 gLCD or a 12x4 cLCD screen in place with a button or two. I began looking at Arduino friendly ADCs and quickly realized that I was a bit out of my depth. Queue idea #2;
The second thought I had was to rig up and simply bury this AD2010 in the device, as it has all the circuitry already in place; an internal 200mV ref, 60Hz rejection, and the target resolution of 100µV. Another fun feature is that it has BCD outputs for each of the digits (1's, 10's, 100's, and 1 000's) as well. So, I can bury this meter in the device and pipe the BCD signals to an Arduino for math and LCD output. Not elegant, but would work for what I need, and I already have 'em.
Is there an ADC out there that I could use in this scenario? (ADC should expect 0~200µA, and display 0~120.0 accordingly, with 1/10th resolution, works out to roughly 166.7nA per 1/10th on the display)